How one entrepreneur turned his high school hobby into a business that makes over $10,000 a month

When he joined the cross country team as a high school freshman in 1998, he says, he was hoping to high jump like he had in middle school, "and my parents told me cross country was like track. Little did I know it's all running — it was a rude awakening."

He liked the team and coach so much that he stuck with it anyway, running all through high school outside of Boston and then through college in Connecticut. When he graduated in 2006 and took on a full-time accounting job in Washington, DC, he says, "I just couldn't give up running. A lot of my teammates got more involved in their jobs, but I kept training competitively."

He changed gears from accounting to consulting, but remembers never feeling like "I was doing something I was really passionate about." After running a marathon in 2008 and suffering from a ligament injury that sidelined him for six months, he turned his thoughts and focus to how he could stay healthy in the long term while still training intensively.

In 2010, Fitzgerald started a personal blog to get more involved in the online community of runners, and in two years had about 4,000 readers subscribed to his email list. "I felt like I had cracked the code of running healthy and I needed to share it with people," the 31-year-old says.

"I decided to work on the blog full-time when it consistently made about the same amount as my day job at the time," he says. "I wasn't married and didn't have kids or any other responsibilities so I figured I might as well give it a go."

Since then, Fitzgerald's blog has evolved into Strength Running, a six-figure online business that earns over $10,000 a month (he doesn't share exact revenue numbers). His profit margins, he estimates, are about 80-90%.

He's become a USATF running coach, and works with all of his clients virtually. Currently, he makes money through four primary offerings:

One-on-one coaching via unlimited emails and phone calls, along with a customized training plan, for $189 a month

A customized training program only for $119 a month, with the option to add a follow-up call for a total of $189

A two-tier nutrition for runners program starting at $79 for an explanation of nutrition and diet philosophies built with a USDA-certified dietitian, or $169 to add on a cookbook and example meal plans as well as insight on how to structure your meals according to the time of day you run

A three-tier injury prevention course starting at $49, then including interviews with elite runners, bestselling authors, and biomechanics experts for $99, as well as a library of training plans and videos for $149

Fitzegerald has run four marathons.Jason Fitzgerald / Strength Running
Fitzgerald says he's in the results business. "I want to make sure they're running the miles they want, and increasing distance at the rate they want. Running isn't everyone's top priority and I recognize and understand that for people with kids and jobs and busy lives, it's important to make sure the training fits around that. A coach comes in and makes sure you're focusing on the most important things you can be doing, and gives structure to your training."

He dedicates about 40 hours a week to his business from his home in Denver, Colorado, where he and his wife moved last year with their now 2-year-old daughter. However, he says, due to the flexibility of his work, he tends to work six or seven days a week, taking mid-mornings off to go for his own runs.

His earnings have allowed his wife to leave her job teaching and stay home while expecting their second child to work on developing an app for children, and have given them the ability to afford traveling to visit family — flying on off-days, because he doesn't keep a standard schedule.

Fitzgerald says the No. 1 thing that contributed to his success was consistency. "From the day I published my first post, I published two articles per week, every week," he says. "It didn't matter if it was Christmas or my honeymoon, it was a consistent schedule. That goes not only for the publication of articles, but also reaching out to other bloggers to build relationships and to coaches asking for opportunities to write guest articles. I've seen a lot of people who want to have some type of online business and work at it for a month, and then get too busy and lose steam. You can't build a business if you're not constantly in it. If you're not thinking about it every day, you probably don't have the chops to get it done."

Do you have a lucrative side gig, a cool career path, or a unique approach to earning money? Email lkane[at]businessinsider[dot]com.